A top Senate Republican on Thursday accused President Trump of illegally refusing to spend $2.9 billion approved by Congress, teaming with Democrats in an early salvo in the simmering struggle between Congress and the White House over which has the ultimate power over federal spending.
Senator Susan Collins, Republican of Maine and the chairwoman of the Appropriations Committee, initiated a letter to the White House that was signed by Senator Patty Murray of Washington, the panel’s senior Democrat. The letter asserted that the administration had violated the six-month spending law approved by Congress earlier this month.
They pointed to a memo Mr. Trump had sent to Congress on Monday that declared that only a portion of the $12.4 billion designated as emergency funding in the legislation would actually be spent, “because I do not concur that the added spending is truly for emergency needs.”
The appropriators vigorously contested that assertion, arguing that the law requires the administration to spend all emergency money or none of it, and does not allow the president to decide for himself what money to spend and what not to.
“Just as the president does not have a line-item veto, he does not have the ability to pick and choose which emergency spending to designate,” the letter said.
They noted that the Trump administration’s interpretation of federal budget law was at odds with how presidents of both parties had viewed it for two decades.
“It is incumbent on all of us to follow the law as written — not as we would like it to be,” Ms. Collins and Ms. Murray wrote.
Documents compiled by the appropriations panel showed that the White House action would deny funding in 11 areas that it has already targeted for elimination or steep reductions, including $750 million in international disaster assistance, $750 million in migration and refugee assistance, $234 million for the National Science Foundation and $100 million for the National Oceanic and Atmospheric Administration, among others.
It also withheld $115 million for international narcotics control and enforcement, a decision singled out by Ms. Collins as particularly confounding.
“Why would you want to do that, given the huge drug problem that we have had?” she said in an interview. “We need the help of other nations to stop that.”
In notifying Congress of his decision on Monday, Mr. Trump questioned the necessity of some of the funding and asserted the authority to allow some money to be distributed while blocking the rest.
He said the spending had been “improperly designated by Congress as emergency,” noting that it had been included as a “side deal” negotiated between Republicans and Democrats in 2023 to allow funding in excess of spending caps.
His decision was accompanied by a memorandum from Russell T. Vought, the head of the Office of Management and Budget, who asserted that the president’s action was justified.
Mr. Trump and Mr. Vought, who also headed the Office of Management and Budget in Mr. Trump’s first administration, argue that the budget law that gives Congress the power to set spending to be executed by the executive branch is unconstitutional. They contend that the president has the power to withhold money even if it was approved by Congress, a proposition likely to be ultimately tested in the courts.
Ms. Murray, in a speech on the Senate floor on Thursday, said the White House and its allies were ignoring a clear constitutional provision that gives Congress the power to set spending.
“Right now we have a couple of billionaires running our country straight into the ground who seem to have skipped American history because President Trump and Elon Musk don’t seem to care much about our Constitution,” she said. She pointed to the provision that “no money shall be drawn from the Treasury but in consequence of appropriations made by law.”
“Their lack of interest in that section of the Constitution doesn’t make it any less real at all,” she said.
The decision by Ms. Collins to challenge the administration was notable since many Republicans on Capitol Hill have been silent on the administration’s attempts to assert extraordinary power over federal spending.
The fight over who has final authority over funding will hang over the coming debate for 2026 spending as the House and Senate assemble allocations for federal agencies.
In the House, Representative Rosa DeLauro of Connecticut, the top Democrat on the Appropriations Committee, also lashed out at the spending edict. But her letter to Mr. Vought was not signed by Representative Tom Cole, the Oklahoma Republican who chairs the panel.
Ms. DeLauro accused Mr. Vought of providing “ineffective and misleading” advice to the president and putting the entire $12.4 billion — including $8 billion for rental assistance backed by both parties and $900 million for NASA — at risk since the law specifically said it was all or nothing.
“If you direct agencies to spend this money you would be requiring them to draw money from the Treasury, absent an appropriation made by law,” she wrote, saying that violation of the budget law carried the risk of fines and other punishment.
Ms. Collins said she and Ms. Murray were relying on legal opinions and findings by the Congressional Research Service that they were in the right and said they hoped to persuade Mr. Vought to reconsider his view.
“The best outcome would be if O.M.B. took a second look at this,” she said.
